The function of the synaptic terminal membrane skeleton in maintenance and modulation of neuronal function is an enigma. Brain spectrin has been identified as a prominent protein in the synaptosome membrane skeleton. The role of brain spectrin in the organization and function of the synaptic terminal membrane skeleton is unknown. The objective of this work is to elucidate the structure and function of the synaptic terminal membrane skeleton and determine its influence on the function of the synaptic terminal. The role of brain spectrin in the organization and function of the membrane skeleton is addressed. The specific aims are threefold: 1) the elucidation of the domain structure of human brain spectrin as defined by chemical and proteolytic cleavage; 2) the identification of new spectrin binding proteins in the synaptic terminal membrane skeleton; and 3) the role of phosphorylation, calcium-activated proteolysis and isoform diversity on the function of brain spectrin. Domain structure will be determined by IEF/SDS-PAGE of digests of brain spectrin and two-dimensional peptide mapping. Functional domains will be identified by in vivo binding assays of radiolabeled brain spectrin digests and two-dimensional peptide mapping. New spectrin binding proteins will be identified by immunoaffinity, immunoprecipitation, solution binding studies, and nondenaturing gel electrophoresis of brain spectrin combined with proteins isolated from various subcellular fractions. Phosphorylation will be performed in situ with specific kinase stimulants, while sites of phosphorylation will be determined by two-dimensional peptide mapping. The sites of calcium activated proteolysis on brain spectrin will be determined; isoforms of brain spectrin will be identified by antibody reactivity, two-dimensional peptide mapping and domain structure. The effects of phosphorylation, proteolysis, and isoform diversity on spectrin function will be determined using in vitro binding assays.